Conventionally, a fluidized bed reactor has been widely used when alkane and/or alkene is subjected to a vapor phase catalytic ammoxidation reaction in the presence of a metal composite oxide catalyst. In a fluidized bed reactor used on an industrial scale, the production operation is continuously carried out for a long period of time, and therefore, a decrease in catalytic activity exerting influence on the reaction yield, reduction of the amount of a catalyst charged due to outflow of the catalyst, and a change in particle size distribution of a catalyst or the like are brought about. On that account, for the purpose of improving a reaction yield of unsaturated nitrile, development of catalysts, improvement in internal equipment of the reactor, etc. have been made.
For example, for the purpose of providing a process for stably producing α,β-unsaturated nitrile such as acrylonitrile in a high yield over a long period of time by suppressing deterioration of a metal oxide catalyst, Patent Literature 1 discloses a vapor phase catalytic oxidation reaction method for hydrocarbon, wherein when alkane having 2 to 8 carbon atoms and/or alkene having 2 to 8 carbon atoms is subjected to a reaction of vapor phase catalytic oxidation using a fluidized bed reactor in the presence of ammonia and a metal composite oxide catalyst, the temperature of a zone where the flow density of the catalyst in the fluidized bed reactor is 50 kg/m3 or less is set to be lower than the temperature of a zone where the catalyst flow density is 300 kg/m3 or more.